In a new application, an young investigator requests five years of support for studies of RPE65, an abundant microsomal associated protein. The major goal of this proposal is to determine if RPE-65 is the retinol isomerase, and if so, to characterize it's activity. Specific Aim 1 is to express human RPE-65 and determine the role of the recombinant protein in retinoid processing. Specific Aim 2 is to determine the amino acids in RPE-65 that are critical for its subcellular localization and retinoid processing activity. Specific Aim 3 is to clone salamander RPE-65 and determine its cellular localization. Specific Aim 4 is to examine the retinoid profile of RPE-65 in vivo using RPE-65 knockout mice that have been generated by a collaborator.